Agree point of overpopulation is not mentioned enough. Someone made an estimate that earth can sustain more than 10 billion but that is provided we all work together. I cannot see that happening providing we have country boarders.
I expect wars starting to happen for resources in the next 10-20 years, not a popular opinion.
wars for resources happen every single day. Why do we even care about the middle east? Because of oil.
Im not sure why you think it is not a popular opinion, it is the status quo.
Water is actually an energy problem. Water is generally not created/destroyed and so energy is the limiting factor. With unlimited energy a city would essentially recycle the vast majority of its water.
The earth can sustain much more than that, we even have the beginnings of the technology needed for that now. Indoor farming can produce the needed food, providing we can produce enough energy - which requires a lot of renewables and some breakthroughs in nuclear fission and fusion. Desalinization can produce the water, with the same energy requirements. In the end everything is an energy problem, which is why nuclear fusion is so exciting.
We're actually limited not by space, water, or arable land, but by thermodynamics. At some point we'd overheat the planet directly from our own waste heat. We have to get off the planet to continue growing the population.
Once we do that the limits on human population are so high as to be mind boggling.
But this is all limited by how people will coexist and if they will work towards the same goal, which rarely happens on a large scale Paris agreement for example
I expect wars starting to happen for resources in the next 10-20 years, not a popular opinion.